1. Field of the Invention
This invention relates to a display apparatus such as a liquid crystal display and an electroluminescent (EL) display, and more particularly to a multi-gray level display apparatus and a method of displaying an image at many gray levels.
2. Background Art
In recent years, a demand has grown for a display apparatus represented by a liquid display, which can display images not only in high-resolution but also at various gray levels.
For example, an active-matrix display having a plurality of pixels and a plurality of switching elements such as thin-film transistors (TFTs), each provided for one pixel, comprises a plurality of pixel electrodes, a common electrode opposing the pixel electrodes, a cell of liquid crystal composition held between the common electrode, on the one hand, and the pixel electrodes, on the other. Generally, in a liquid crystal display of this type, a drive voltage is applied to selected ones of the pixel electrodes for each one-frame period, thereby to display an image.
In order to display an image at, for example, 64 (=26) gray levels, it is necessary to use as many as 64xc3x972 different voltage levels. This is because the display needs to be AC-driven for the purpose of preventing deterioration of the liquid crystal composition used.
To provide a drive voltage having 64xc3x972 different voltage levels is to increase power consumption in the drive-circuit IC incorporated in the display or the manufacturing cost of the display. Hence, this method of driving the display is not desirable.
Another display-driving method known is pulse-width modulation. In this method, the time for applying a drive voltage to a pixel, i.e., the pulse width of the drive voltage, not the level of the drive voltage, is changed in accordance with the gray level at which to display the pixel.
Pulse-width modulation, however, requires a complex drive circuit and is difficult to be controlled in order to display an image at as many as 64 (=26) gray levels.
To solve these problems to display multi-gray level images, frame-rate control (FRC) has been developed recently. This control method controls the number of consecutive frame (F) periods constituting one display period during which a drive voltage at a preset level is applied to the pixel electrode to turn on a pixel. Jpn. Pat. Appln. KOKAI Publication No. 2-115893 discloses a technique of preventing flicker on a liquid crystal display to which the FRC method is applied. In the technique, a block of neighboring pixels is determined as a unit to be controlled, and the number of frame (F) periods constituting one display period is variably set between the pixels to be turned on.
With the above-mentioned FRC method it is not necessary to change the level of the drive voltage, and it is possible to solve the problems inherent in the pulse-width modulation.
To display images at more different gray levels by means of the FRC method, however, it is necessary to further increase the number of frame (F) periods which constitute one display period. If an image is displayed at, for example, 64 (=26) gray levels, the number of frame (F) periods will increase so much that the image can no longer be recognized as a multi-gray level one or may be deteriorated with flicker.
The present invention has been made to solve the technical problems described above. The objective of the present invention is to provide a display apparatus for displaying multi-gray level images without lowering their quality or causing flicker on them, and also a method of displaying an image at many gray levels.
A first aspect of this invention is, a multi-gray level display apparatus which performs an image display by selecting one of preset voltage levels in accordance with input multi-gray level display data. The apparatus comprises a display panel having a plurality of pixels; a first gray-level pattern generating circuit for generating a first gray-level pattern which acquires a gray level during m frame periods (m is a positive integer not less than 2); a second gray-level pattern generating circuit for generating a second gray-level pattern which acquires another gray level during n frame periods (n is a positive integer greater than m); and selection control means for selecting and outputting one of the preset voltage levels, based on an output from the first or second gray-level pattern generating circuit when the input multi-gray level display data corresponds to a gray level of either the first gray-level pattern or the second gray-level pattern.
An second aspect of the invention is a multi-gray level display apparatus which performs an image display in accordance with input k-bit multi-gray level display data (k is a positive integer greater than 2). The apparatus comprises a display panel having a plurality of pixels; a gray-level voltage generating circuit for generating 2i gray-level voltages (i is a positive integer less than k+1); a first gray-level pattern generating circuit for generating a first gray-level pattern which acquires a gray level during m frame periods (m is an integer not less than 2); a second gray-level pattern generating circuit for generating a second gray-level pattern which acquires another gray level during n frame periods (where n is an integer greater than m); and selection control means for converting the k-bit multi-gray level display data to (ixe2x88x921)-bit multi-gray level display data corresponding to one of the voltage levels, and outputting the (ixe2x88x921)-bit multi-gray level display data, when the multi-gray level display data corresponds to the one voltage level.
A third aspect of the invention is a multi-gray level display apparatus which performs an image display in accordance with input k-bit multi-gray level display data (k is a positive integer greater than 2). The apparatus comprises a display panel having a plurality of pixels; a gray-level voltage generating circuit for generating a gray-level voltage of 2i voltage levels (i is a positive integer less than k+1); a first gray-level pattern generating circuit for generating a first gray-level pattern which acquires a gray level during m frame periods (m is an integer not less than 2); a second gray-level pattern generating circuit for generating a second gray-level pattern which acquires another gray level during n frame periods (where n is an integer greater than m); and selection control means for converting the k-bit multi-gray level display data to (ixe2x88x921)-bit multi-gray level display data corresponding to one of the voltage levels based on an output from the first or second gray-level pattern generating circuit, and outputting the (ixe2x88x921)-bit multi-gray level display data, when the multi-gray level display data corresponds to a gray level of either the first gray-level pattern or the second gray-level pattern.
A fourth aspect of the invention is a multi-gray level display apparatus which comprises: a display panel having a plurality of pixels each of which is driven by a voltage selected from a group of voltages in accordance with multi-gray level display data; a first gray-level pattern generating circuit for generating a first gray-level pattern which acquires a gray level during m frame periods (m is an integer not less than 2); a second gray-level pattern generating circuit for generating a second gray-level pattern which acquires another gray level during n frame periods (where n is an integer greater than m); display data converting means for converting input k-bit multi-gray level display data (k is a positive integer greater than j) to j-bit multi-gray level display data; and an operation circuit for performing an operation on the j-bit multi-gray level display data in accordance with the first gray-level pattern when the k-bit multi-gray level display data corresponds to a display gray level based on the first gray-level pattern, and in accordance with the second gray-level pattern when the k-bit multi-gray level display data corresponds to a display gray level based on the second gray-level pattern, and for outputting a result of the operation thus performed.
A fifth aspect of this invention is a method of displaying multi-gray level images by selecting one of preset voltages in accordance with input multi-gray level display data, in which one of the preset voltages is selected and output in accordance with an output of a first gray-level pattern generating circuit for generating a first gray-level pattern which acquires a gray level during m frame periods (m is a positive integer not less than 2), or in accordance with an output of a second gray-level pattern generating circuit for generating a second gray-level pattern which acquires another gray level during n frame periods (n is a positive integer greater than m), when the input multi-gray level display data corresponds to a voltage between first and second of the preset levels, the second level being lower than the first.
A sixth aspect of the invention is a method of displaying multi-gray level images in accordance with input k-bit multi-gray level display data (k is a positive integer greater than 2). The k-bit multi-gray level display data corresponds to one of preset 2i voltages (i is a positive integer less than k+1). The k-bit multi-gray level display data is converted to (ixe2x88x921)-bit multi-gray level display data corresponding to the one of the preset voltages and the (ixe2x88x921)-bit multi-gray level display data is output, and when the k-bit multi-gray level display data corresponds to none of the preset voltages, the k-bit multi-gray level display data is converted to (ixe2x88x921)-bit multi-gray level display data in accordance with an output and the (ixe2x88x921)-bit multi-gray level display data is output, the output being either of a first gray-level pattern generating circuit for generating a first gray-level pattern which acquires a gray level during m frame periods (m is an integer not less than 2) or a second gray-level pattern generating circuit for generating a second gray-level pattern which acquires another gray level during n frame periods (where n is an integer greater than m).
A seventh aspect of this invention is a multi-gray level display apparatus in which one of preset voltages is selected in accordance with input multi-gray level display data, thereby to display an image at gray levels. The apparatus comprises: a display panel having a plurality of pixels; a first gray-level pattern generating circuit having a first gray-level pattern which acquires a gray level during m frame periods (m is a positive integer not less than 2); a second gray-level pattern generating circuit having a second gray-level pattern which acquires another gray level during m frame periods and which differs from the first gray-level pattern; and selection control means for selecting and outputting one of the preset voltages, in accordance with an output from the first or second gray-level pattern generating circuit when the input multi-gray level display data corresponds to a gray level of either the first gray-level pattern or the second gray-level pattern.
An eighth aspect of the invention is a multi-gray level display apparatus which comprises: a display panel having a plurality of pixels each of which is driven by a voltage selected from a group of voltages in accordance with multi-gray level display data; a first gray-level pattern generating circuit for generating a first gray-level pattern which acquires a gray level during m frame periods (m is an integer not less than 2); a second gray-level pattern generating circuit for generating a second gray-level pattern which acquires another gray level during m frame periods and which differs from the first gray-level pattern; display data converting means for converting input k-bit multi-gray level display data (k is a positive integer greater than j) to j-bit multi-gray level display data; and an operation circuit for performing an operation on the j-bit multi-gray level display data in accordance with the first or second gray-level pattern when the k-bit multi-gray level display data corresponds to a display gray level based on the first or second gray-level pattern, and for outputting a result of the operation thus performed.
A ninth aspect of this invention is a method of displaying multi-gray level images in accordance with input k-bit multi-gray level display data (k is a positive integer greater than 2). When the k-bit multi-gray level display data corresponds to a preset voltage, the k-bit multi-gray level display data is converted to i-bit multi-gray level display data (i is a positive integer less than k) corresponding to the preset voltage and the i-bit multi-gray level display data is output. and when the k-bit multi-gray level display data corresponds to none of the preset voltages, the k-bit multi-gray level display data is converted to i-bit multi-gray level display data in accordance with an output and the i-bit multi-gray level display data is output. The output is either of a first gray-level pattern generating circuit for generating a first gray-level pattern which acquires a gray level during m frame periods (m is an integer not less than 2) or a second gray-level pattern generating circuit for generating a second gray-level pattern which acquires another gray level during m frame periods and which differs from the first gray-level pattern.
A tenth aspect of this invention is a multi-gray level display apparatus in which one of preset voltages is selected in accordance with input multi-gray level display data to display an image at gray levels. The apparatus comprises: a display panel having a plurality of pixels; a first gray-level pattern generating circuit for generating a first gray-level pattern which acquires a gray level during m frame periods (m is a positive integer not less than 2) and which is provided for a plurality of pixels controlled as a unit and arranged in a first pattern; a second gray-level pattern generating circuit for generating a second gray-level pattern which acquires a gray level during m frame periods and which is provided for a plurality of pixels controlled as another unit and arranged in a second pattern different from the first pattern; and selection control means for selecting and outputting one of the preset voltages in accordance with an output from the first or second gray-level pattern generating circuit when the input multi-gray level display data corresponds to a gray level of either the first gray-level pattern or the second gray-level pattern.
A eleventh aspect of this invention is a multi-gray level display apparatus in which one of preset voltages is selected in accordance with input multi-gray level display data, to display an image at gray levels. The apparatus comprises: a display panel having at least a plurality of red pixels, a plurality of blue pixels and a plurality of green pixels; a first gray-level pattern generating circuit for generating a first gray-level pattern which acquires a gray level during m frame periods (m is a positive integer not less than 2) and which is provided for the plurality of red pixels controlled as a first unit; a second gray-level pattern generating circuit for generating a second gray-level pattern which acquires a gray level during m frame periods and which is provided for the plurality of green pixels controlled as a second unit; a third gray-level pattern generating circuit for generating a third gray-level pattern which acquires a gray level during m frame periods and which is provided for the plurality of blue pixels controlled as a third unit; and selection control means for selecting and outputting one of the preset voltages in accordance with an output from the first, second or third gray-level pattern generating circuit when the input multi-gray level display data corresponds to a gray level of the first gray-level pattern, the second gray-level pattern or the third gray-level pattern.
A twelfth aspect of the invention is a multi-gray level display apparatus in which one of preset voltages is selected in accordance with input multi-gray level display data to display an image at gray levels. The apparatus comprises: a display panel having at least a plurality of red pixels, a plurality of blue pixels and a plurality of green pixels; a gray-level pattern generating circuit for generating a gray-level pattern which acquires a gray level during m frame periods (m is a positive integer not less than 2) and which is provided for a group of pixels, including red, blue and green pixels which are controlled as a unit; and selection control means for selecting and outputting one of the preset voltages in accordance with an output from the gray-level pattern generating circuit when the input multi-gray level display data corresponds to a gray level of the gray-level pattern.
A thirteenth aspect of the invention is a multi-gray level display apparatus in which one of preset voltages is selected in accordance with input multi-gray level display data, thereby to display an image at gray levels. The apparatus comprises: a display panel having a plurality of pixels; a first gray-level pattern generating circuit for generating a first gray-level pattern which acquires a gray level during m frame periods (m is a positive integer not less than 2); a second gray-level pattern generating circuit for generating a second gray-level pattern which acquires another gray level during m frame periods; and selection control means for selecting and outputting at least one of the preset voltages or a preset voltage adjacent thereto in accordance with the first gray-level pattern when the input multi-gray level display data corresponds to a gray level of the first gray-level pattern, and selecting and outputting at least one of the preset voltages or a preset voltage next to the preset voltage which is adjacent to the at least one of the preset voltage, in accordance with the second gray-level pattern when the input multi-gray level display data corresponds to a gray level of the second gray-level pattern.
A fourteenth aspect of the invention is a method of displaying multi-gray level images by using a plurality of pixels, in accordance with input multi-gray level display data, wherein when the input multi-gray level display data corresponds to a gray level of a first gray-level pattern which acquires a gray level during m frame periods (m is a positive integer not less than 2), at least one of the preset voltages or a preset voltage adjacent thereto is selected and output in accordance with the first gray-level pattern, and when the input multi-gray level display data corresponds to a gray level of a second gray-level pattern which acquires a gray level during m frame periods, at least one of the preset voltages or a preset voltage next to the preset voltage which is adjacent to the at least one of the preset voltage is selected and output in accordance with the second gray-level pattern.
A fifteenth aspect of the invention is a multi-gray level display apparatus in which one of preset voltages is selected in accordance with input multi-gray level display data, thereby to display an image at gray levels. The apparatus comprises: a display panel having a plurality of pixels; a gray-level pattern generating circuit for generating a gray-level pattern which acquires a gray level during m frame periods (m is a positive integer not less than 2); and selection control means for selecting and outputting one of the preset voltages in accordance with the gray-level pattern when the input multi-gray level display data corresponds to a gray level of the gray-level pattern.
In the apparatuses and methods according to the first to sixth aspects of the present invention, two gray-level pattern garnering circuits are used. The first circuit generates a first gray-level pattern which acquires a gray level during m frame periods (m is a positive integer not less than 2). The second circuit generates a second gray-level pattern which acquires another gray level during n frame periods (n is a positive integer greater than m).
Input multi-gray level display data is converted to correspond to a preset voltage in accordance with an output of the first or second gray-level pattern generating circuit when the input gray-level display data corresponds to the display gray level of either the first gray-level pattern or the second gray-level pattern. Therefore, it is possible to display an image having a gray level other than the preset voltage.
As described above, the preset voltage is selected in accordance with the multi-gray level data and also with the output of the first or second gray-level pattern generating circuit which are controlled during different frame (F) periods. The number of frame (F) periods to be controlled need not be greatly increased to display multi-gray level images. Hence, multi-gray level images can be displayed without lowering their quality or causing flicker on them.
As indicated above, in the apparatuses and methods according to the seventh to ninth aspects of the present invention, two gray-level pattern generating circuits are used. The first gray-level pattern generating circuit generates a first gray-level pattern which acquires a gray level during m frame periods (m is a positive integer not less than 2). The second gray-level pattern generating circuit generates a second gray-level pattern which differs from the first gray-level pattern.
Input multi-gray level display data is converted to correspond to a preset voltage in accordance with an output of the first or second gray-level pattern generating circuit when the input gray-level display data corresponds to the display gray level of either the first gray-level pattern or the second gray-level pattern. It is possible to display an image having a gray level other than the preset voltage.
Since a gray level is controlled in accordance with at least two different gray-level patterns, multi-gray level images can be displayed without lowering their quality or causing flicker on them.
As described above, in the apparatuses and methods according to the tenth to twelfth aspects of the invention, a plurality of pixels arranged in a first pattern are controlled as a unit during m frame periods (m is a positive integer not less than 2) to acquire a gray level, and a plurality of pixels arranged in a second pattern are controlled as a unit during m frame periods to acquire a gray level.
Since the pixels are controlled in two or more different units, the pixels of each unit can be controlled in the way best possible to display an image. This makes it possible to display a multi-gray level image by using less voltages than otherwise.
In a display apparatus which has at least red (R) pixels, green (G) pixels and blue (B) pixels and which can therefore display color images, pixels including red, blue and green pixels are controlled as a unit, or red pixels, green pixels and blue pixels are controlled as respective units. This makes it possible to display multi-gray level images of high quality by using less voltages than otherwise.
As described above, in the apparatuses and methods according to the thirteenth and fourteenth aspects of the invention, at least one of the preset voltages or a preset voltage adjacent thereto is selected and output in accordance with a first gray-level pattern when input multi-gray level display data corresponds to a gray level of the first gray-level pattern, and at least one of the preset voltages or a preset voltage next to the preset voltage which is adjacent to the at least one of the preset voltage is selected and output in accordance with a second gray-level pattern when the input multi-gray level display data corresponds to a gray level of the second gray-level pattern. The number of frame (F) periods to be controlled need not be greatly increased to display multi-gray level images. Multi-gray level images can therefore be displayed without lowering their quality or causing flicker on them.
As indicated above, the apparatus according to the fifteenth aspect of the present invention comprises, a gray-level pattern generating circuit for generating a gray-level pattern which acquires a gray level during m frame periods (m is a positive integer not less than 2).
Input multi-gray level display data is converted to correspond to a preset voltage in accordance with an output of the gray-level pattern generating circuit when the input gray-level display data corresponds to the display gray level of the gray-level pattern. It is possible to display an image having a gray level other than the preset voltage.
Since the preset voltage is selected in accordance the preset voltage is selected in accordance with the multi-gray level data and also with the output of the first or second gray-level pattern generating circuit which are controlled during different frame (F) periods. The number of frame (F) periods to be controlled need not be greatly increased to display multi-gray level images. Hence, multi-gray level images can be displayed without lowering their quality or causing flicker on them.